1. Field of the Invention
The present invention relates to an image forming apparatus for forming a visible image, an image forming method and a medium.
2. Description of the Related Art
Some widely used image forming apparatuses determine in every image forming process whether an image corresponds to a blank sheet or not or whether an image is color or monochrome, and manage the total output number of color images and that of monochrome images. A sum based on a determination result in such an image forming apparatus is used for output management, output limitation, running cost grasping, maintenance, charging management, and the like.
An image forming apparatus receives PDL data (page description data), interprets it, and generates image data for image formation. The image data is sometimes divided into, for example, tile-shaped small areas and sequentially generated together with additional information. Each of the generated image data of the divided small areas is sequentially processed, compressed, and stored in a memory based on the additional information. Since the image data is compressed before it is stored in the memory, the memory capacity can be saved. Generally, the additional information easily includes, for example, information representing whether one of the sequentially generated image data of the divided small areas has the same contents as those of immediately precedingly generated image data. When image data necessary for image formation of a full page are written in the memory, the image forming apparatus forms an image using these image data.
Conventionally, after scanning the color information of image data of a small area or full page that is an image formation target, it is determined whether the color information contains a color component, thereby determining whether the result of visible image formation is a blank sheet. Japanese Patent Laid-Open No. 2002-120411 describes a technique of executing a blank sheet detection process for only K component image data, compressing the K component image, and comparing the data size of the compressed K component image with that of compressed YMC component image data, thereby performing blank sheet determination of a color image at a high speed. Japanese Patent Laid-Open No. 2004-227530 describes a technique of compressing image data of an output target, and comparing the compressed data with blank image data prepared in advance, thereby executing blank sheet determination. Japanese Patent Laid-Open No. 2004-147193 describes an image processing apparatus capable of executing blank sheet determination of a document using an existing compression/decompression means without adding a new functional circuit. According to Japanese Patent Laid-Open No. 2004-147193, since unnecessary image data determined as a blank sheet document is erased from a storage medium such as a memory, the area of the storage medium is effectively usable.
However, in determining whether the result of visible image formation is a blank sheet, if the color information of all the sequentially generated image data is scanned by software processing, as in the prior art, the process time increases. To scan the color information of image data, uncompressed image data needs to be prepared. This requires a larger memory capacity. In the conventional techniques, whether an image formation result is a blank sheet is determined on the basis of the interpretation result of a PDL data (page description data) interpretation module implemented by software. However, since the determination is done using PDL data without solving depth information (Z direction), a determination error may occur. If blank sheet determination is done by hardware to solve the problem, the cost of the image forming apparatus rises due to the added hardware. The method of determining based on a compression rate whether image data is a blank sheet document may cause a determination error because a black sheet filled with black color information and a blank sheet filled with white color information have almost the same compression rate.